1. Field of the Invention
The present invention relates to a communication control apparatus and a method therefor, and more particularly to such an apparatus and a method for use in a system in which data is transmitted and received between a number of communication nodes spatially distributed or installed on mobile bodies, such as a system that is constituted by a plurality of communication devices connected to a sensor network or local area network (LAN).
2. Description of the Background Art
There are various methods for avoiding the collision of communication data, in which individual nodes allocate time slots autonomously without a central administrative server. Such methods are disclosed in U.S. Patent Application Publication Nos. US 2005/0190796 A1 to Date et al., US 2006/0114841 A1 to Date et al., and US 2006/0114840 A1 to Date et al., and Japanese Patent Laid-Open Publication Nos. 2006-074617 and 2006-074619, for example.
In these conventional methods, each node transmits and receives impulse signals periodically to and from its neighboring nodes, whereby communication timings are mutually adjusted. An impulse signal is a control signal indicating the transmission timing of its own node. This establishes time slot allocation, which divides one period during which an impulse signal is transmitted into sections approximately equal to each other, between nodes within an interaction range that impulse signals can reach. That is a telecommunications system in which the chances of transmission are equally given to each node within the interaction range. For instance, consider the case where three nodes A, B, and C lie within a sensor network. Node A establishes time-slot allocation, which approximately equally divides one oscillation period T, between itself and other nodes such as nodes B and C within the interaction range. If all nodes on networks operate in this manner, then it becomes possible to transmit sensing data from each node to a sink node with multiple hops. The sensing data is of a data signal that is transmitted in a time slot.
In the case of employing the methods disclosed in the above-mentioned five prior art documents, however, unequal time-slot allocation which gives time slots to particular nodes at higher rates is performed than the remainings. In such a telecommunications system in which the chances of transmission are given unequally between nodes, some problems will arise. The first problem is that the transmission of an impulse signal will collide with that of a data signal. The second problem is that it will be difficult to freely control the ratio of the size of a time slot that is allocated to each node. Particularly, it is fairly difficult to allocate a time slot having a much greater ratio.
The applicant of the patent application has proposed a solution to the first problem. Even with this proposed solution, the second problem could not be solved.